Foamed synethetic resin materials in which a foamed core blends in the outward direction into outer layers, which are densified relative to a foamed core, are well known. The densified outer layers consist of the same synthetic resin as the foamed core. These outer layers can be densified almost up to the theoretical maximum density of the material. These cellular synthetic resins are referred to as "structural foam material" or "integral foam material".
It is known to produce synthetic resin materials as imitation wood. A sheet of synthetic resin is brought to an elevated temperature, for example, by means of surface heating and fine furrows are embossed in the surface of the material by a cold embossing instrument, such as a press die or an embossing roller. In this way, the texture or grain of wood is to be imitated. The embossing of the texture furrows produces difficulties. In general, the required embossing pressure is so large that no sufficiently uniform embossing pattern can be obtained, especially if the plastic to be embossed has a thickness beyond normal sheet thickness. Specifically, the heating of such a plate or sheet cannot be made to proceed so far that the thermoplastic synthetic resin is sufficiently softened for use of a low embossing pressure, because there would then be a danger that the material during the application of the embossing force, if not before, would cave in, become warped or deformed--especially if the material is a plate with a hollow profile. Hollow-profile plates are not sufficiently capable of retaining their overall flatness in such circumstances.
Plates of imitation wood have already been produced out of structural or integral foam. Flow lines are produced during the simultaneous production of the foamed core and the densified outer layers. The flow lines, which are intended to imitate wood grain, are produced in the outer surface of the densified outer layers. The production of the flow lines includes pigmenting and controlling the feeding head and the manner of casting.
In contrast to castings made of homogeneous plastic, imitation wood integral foam castings have the advantage that the specific gravity and the material-working properties are quite similar to those of wood itself. Accordingly, such integral foam cast bodies can be planed, milled, cut, drilled, bolted and nailed without cleaving or splitting the material. However, in the case of injection molding, the shapes of the flow lines cannot be controlled such that the flow lines actually look like true wood grain. Also, the flow lines do not have the three-dimensional character of the fine furrows of natural wood. Therefore, the known imitation wood plates are readily perceivable as being imitations. Additionally, such imitation wood plates do not have the feel of wood.
To eliminate these disadvantages, it has also been proposed that imitation wood beams and the like be molded using molds whose surfaces have a texture resembling that of natural wood. Such imitations look deceptively similar after a suitable staining. However, the cost of production is great. Also, disadvantegously, all the articles produced have identical shape and size.